JP3419658B2 - Demodulator for digital wireless communication - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wireless communication system for performing communication with a signal frequency-modulated or phase-modulated by a digital signal, and more particularly to a differential encoding system as a modulation system,
For example, the present invention relates to a demodulation device used in a base station and a terminal station of a wireless communication system that employs a π / 4 shift differential QPSK system or the like.

[0002]

2. Description of the Related Art In recent years, expectations for a digital automobile / mobile phone system to be compatible with multimedia such as effective utilization of frequency resources and speeding up of data transmission are increasing. The digital transmission system is
It is easy to achieve high transmission quality, high reliability, and high confidentiality using error correction technology, and since it is not necessary to reproduce the faithful transmission waveform and spectrum like analog transmission, it can be used for narrowing bandwidth and multiplexing. It is suitable, and since it can handle voice, images, data, etc. in an integrated and seamless manner, it is attracting attention as one of the communication methods indispensable for the future multimedia information society. In addition, the rapid spread of information access services using personal computers and the decrease in communication charges as seen in personal computer communications and the Internet in recent years have further spurred the spread of digital automobiles / cell phone systems, It is expected that the number of users will continue to increase.

By the way, at present, among mobile phone terminals represented by PHS and PDC, quite small ones having a size of 100 cc or less and a weight of 100 g or less have appeared. The miniaturization of such terminals is approaching the limit in existing digital transmission systems.

Generally, a quadrature demodulation system as shown in FIG. 6 is adopted in a demodulator of a base station and a terminal station of a radio communication system which communicates with a signal which is frequency-modulated or phase-modulated by a digital signal. In this quadrature demodulation type demodulation device, a signal received by an antenna 81 is orthogonal to a base band signal (in-phase component and in-phase component and in-phase component) in a portion including a frequency conversion means 82, a mixer 83, a π / 2 phase shifter 90 and a local oscillator 89. Frequency conversion to quadrature phase component),
Low-frequency wave leaker (LPF) for each phase (channel)
84, AD converter (ADC) 85, root roll-off filter (RROF) 86, delay detector 87 and determination /
AD conversion, band limitation and detection demodulation are performed through the demodulation processing unit 88, and the overall circuit scale becomes large.

Further, in the case of the differential modulation system adopted in PHS or PDC, in order to realize the complex multiplication process for differentially detecting the quadrature baseband signal, as shown in FIG. The detector 87 has four multipliers 92 and 2
It is necessary to prepare one adder 93, which also increases the overall circuit scale. Due to such circumstances, the adoption of the quadrature demodulation method for mobile phones is being shunned. Further, even a software receiver based on a DSP, which has recently received a lot of attention, consumes a lot of instructions in the differential detection processing, so that it is desired to reduce the processing amount.

From the above point of view, the IF demodulation method, which directly extracts the phase component from the received signal in the intermediate frequency band (IF) and performs the detection processing, is actively adopted instead of the orthogonal demodulation method. The advantages of this method are as follows.

(1) No need for frequency conversion to orthogonal baseband IF signal distributor and mixer (×
2), π / 2 phase shifter, local oscillator, low-pass filter (× 2), etc. are unnecessary.

(2) AD converter unnecessary The AD converters for the in-phase component and the quadrature component of the baseband signal, which are indispensable for the quadrature demodulation method, are unnecessary.

(3) Digital filter unnecessary The digital low-pass filters for the in-phase component and the quadrature-phase component of the baseband signal, which are indispensable for the quadrature demodulation method, are unnecessary.

(4) No need for complex differential detection (differential detection) In the quadrature demodulation method, since the baseband signal is treated as a complex signal, the differential detection process requires four multiplication processes and two addition processes. Although it needs to be performed, if the phase component is directly extracted from the IF received signal, the differential detection process can be realized by one subtraction process. (5) In the low-quantization accuracy quadrature demodulation method, since the amplitude components of the orthogonally decomposed received signal are handled, the dynamic range must be set large considering the amplitude fluctuation due to fading,
High quantization accuracy is required. On the other hand, if the phase component is directly extracted from the IF reception signal, the dynamic range for the phase component of 0 to 2π can be set regardless of the amplitude component. For this, at most 5 to 6 bits is sufficient.

As described above, the IF demodulation system has many advantages as compared with the conventional quadrature demodulation system. Therefore, the IF demodulation system is a core technology not only in PHS and PDC but also in the field of personal communication which is expected to grow in the future. obtain.

Mobility is being pursued in future personal communication terminals including car phones and mobile phones. Achieving high quality communication while moving is quite strict, and there is an increasing need to make the communication system itself resistant to movement. The differential modulation method has been attracting attention as one of means for solving the requirement of mobile reception, and has been adopted in many communication systems. This differential modulation method is a type of phase modulation, and is achieved by mapping transmission information to a relative phase (phase difference) instead of mapping transmission information to an absolute phase. As a result, extremely strong resistance to fading distortion peculiar to mobile reception can be provided.

However, although the asynchronous differential demodulation method with respect to the differential modulation method can be realized with a simple structure, the reception S /
N is slightly inferior. Therefore, a synchronous detection method that can improve the reception characteristics is being studied. The synchronous detection method is 2 to 3 (dB) more than the differential detection (differential demodulation) method which is an asynchronous detection method.
Some improvement in reception characteristics can be expected. However, on the other hand,
There is a problem that the process for synchronizing the receiver with the transmitter becomes complicated.

Further, in general, the differential demodulation system adopts a "shift system" in which a fixed amount of phase change is added for each transmission information cycle when mapping transmission information, so that detection is performed for each physical information transmission cycle. It is necessary to switch the judgment criterion at that time, which complicates the configuration of the demodulator.

[0015]

As described above, in a demodulator of a wireless communication system for communicating with a signal frequency-modulated or phase-modulated by a digital signal, various new techniques are applied to reduce the size and power consumption. Is planned,
The demand for lowering the price and extending the call / standby time is being met. However, in order to support multimedia communication, improvement of communication quality is indispensable in addition to these demands. In the shift type differential modulation system, which is a type of phase modulation system that is widely used in mobile communication at present, although the asynchronous detection system is used as the IF demodulation system for the reason described above, the reception characteristic is deteriorated. It's a problem.
Therefore, although the adoption of a synchronous detection method instead of this is being considered, in the shift type differential modulation method, the code determination reference must be changed in the information transmission cycle unit in the detection determination processing section, which complicates the configuration. There was a problem that it would be something.

The present invention has been made to solve the above problems, and it is a wireless communication system that performs communication with a signal that is frequency-modulated or phase-modulated by a digital signal, and more particularly, a wireless communication system that uses a shift-type phase modulation method. A demodulator for digital wireless communication, which does not require control of a code determination reference for each information transmission cycle when a coherent detection system is realized by a demodulator of a base station or a terminal station of a communication system and can simplify the configuration of the device. For the purpose of providing.

[0017]

Means for Solving the Problems] To achieve the above object, a digital radio communication demodulation device of the present invention, [pi
/ N shift differential N-phase PSK modulation type digital wireless communication
In the credit demodulation device, receiving means for receiving a signal frequency-modulated or phase-modulated by a digital signal,
Frequency conversion means for converting the received signal into a signal of a predetermined intermediate frequency, and a unit cycle time of a physical information transmission cycle
About ± π / N between the received signal of the intermediate frequency after the error
Counting means that operates with a predetermined reference clock at a cycle set to a value that causes a phase shift, and sampling that samples the output of the counting means with reference to the received signal of the intermediate frequency and outputs the phase information of the received signal. Means, a detection means for detecting the output of the sampling means, and a demodulation means for demodulating the transmission information from the output of the detection means are provided.

The demodulation for digital radio communication of the present invention
The device is a π / 4 shift differential QPSK modulation type digitizer.
In the demodulator for wireless communication,
Reception that receives a frequency-modulated or phase-modulated signal
Means for converting the received signal into a signal of a predetermined intermediate frequency
Frequency conversion means for conversion and unit cycle of physical information transmission cycle
± π / 4 between the received signal at the intermediate frequency after the expiration of the period
The specified reference clock frequency is set to the value that causes the phase shift of
Counting means operating by lock and output of the counting means
By sampling the received signal of the intermediate frequency as a reference
Sampling means for outputting phase information of the received signal,
Detecting means for detecting the output of the sampling means;
A demodulation means for demodulating the transmission information from the output of the detection means.
It is characterized by having.

By setting the counting cycle of the counting means in this way, it is possible to absorb the phase shift peculiar to the shift type differential modulation method that occurs at each physical information transmission cycle while avoiding the degeneration of the phase of the intermediate frequency reception signal. The detection / judgment can be performed under a fixed judgment criterion without changing the code judgment criterion in units of physical information transfer cycle. This allows
The demodulator for digital wireless communication can be downsized and the power consumption can be reduced.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a demodulator for digital radio communication according to an embodiment of the present invention, that is, a demodulator applied to a base station or a terminal station of a radio communication system for communicating with a signal phase-modulated by a digital signal. It is a figure which shows the structure of.

As shown in the figure, the demodulation device 1 of the present embodiment comprises a receiving antenna 2, a frequency conversion means 3, a phase detection means 4, a sampling means 5, a detection means 6 and a demodulation means 7.

The phase-modulated signal received by the receiving antenna 2 connected to the demodulator 1 is converted into frequency conversion means 3.
Is converted into a signal of a predetermined intermediate frequency. Although omitted in the figure, the frequency conversion means 3 is composed of, for example, a local unit, a clock generator, a mixer, a band limiting filter, an amplifier, and the like. The received signal of the intermediate frequency that has been frequency-converted by the frequency conversion means 3 is input to the sampling means 5. The sampling means 5 samples the output signal of the phase detection means 4 described later with reference to the received signal of the intermediate frequency input from the frequency conversion means 3 and obtains it as the phase information of the received signal of the intermediate frequency.

The phase detecting means 4 comprises a reference clock generating means 9 and a counting means 8 which operates with the reference clock generated by the reference clock generating means 9. A predetermined counting cycle is set in the counting means 8, and the counting means 8 executes counting of the reference clock 9 while repeating resetting at the set counting cycle, and outputs the count value to the sampling means 5.

The counting cycle of the counting means 8 is set to a value different from (the center frequency of) the intermediate frequency and a specific value depending on the shift type differential modulation method. For example, in the case of the π / 4 shift differential QPSK modulation method, the counting cycle of the counter 8 has a phase shift of ± π / 4 from the intermediate frequency reception signal after the unit cycle time of the physical information transmission cycle. It is set to the value that will occur. Similarly, when the π / 2 shift, π / 8 shift, π / 16 shift differential QPSK modulation method is adopted, the counting cycle of the counter 8 is set to an intermediate value after the unit cycle time of the physical information transmission cycle has elapsed. It may be set to a value that causes a phase shift of ± π / 2, ± π / 8, or π / 16 from the frequency reception signal.

FIG. 2 shows the structure of the demodulating device 1 including the detailed structure of the sampling means 5. As shown in the figure, the sampling means 5 comprises an amplitude limiting means 10 for limiting the amplitude of the intermediate frequency reception signal output from the frequency converting means 3 and a holding means 21. Holding means 21
Can be realized by, for example, a D-type flip-flop 22. The D input terminal of the D type flip-flop 22 is connected to the output terminal of the counting means 8 and CLK
The input terminal is connected to the output terminal of the amplitude control means 10. That is, the intermediate frequency reception signal output from the frequency conversion means 3 is shaped like a rectangular wave by being limited to a constant amplitude by the amplitude limiting means 10, and the modulation component of the intermediate frequency reception signal is converted into PWM. It The D type flip-flop 22 holds m-bit data, which is the phase information of the intermediate frequency reception signal output from the counting means 8, for each rising edge of the output signal of the amplitude limiting means 10.

The output signal of the sampling means 5 is information indicating the phase component of the intermediate frequency received signal, and the output signal of the sampling means 5 is detected by the detection means 6 according to the modulation method. The reception signal detected by the detection means 6 is output to the demodulation means 7, and the demodulation means 7 reconfigures the transmission information sequence by performing predetermined demapping processing, parallel serial conversion, etc. on the reception signal. To do.

FIG. 3 is a diagram showing the relationship between the counting cycle of the counting means 8, the physical information transmission cycle, and the cycle of the intermediate frequency reception signal output from the frequency converting means 3.

Here, T is a physical information transmission period (generally called a symbol period). In the case of the shift differential modulation method, even if the same information is transmitted, a constant phase change always occurs after 1T time, and if the IF reception signal is observed at the center frequency of the IF reception signal, the phase is a constant amount θ after 1T time. It only looks ahead or behind. As described above, the demodulation device of this embodiment uses the π / 4 shift differential QPS.
In the π / N shift differential N-phase PSK modulation system such as the K modulation system, the phase difference between the counting cycle of the counting means 8 and the IF reception signal after a unit cycle time of the physical information transmission cycle is ± π.
By setting the value to be / N, the above phase shift is absorbed.

The principle of the present invention will be described by mathematical expressions.

Cos (ω _c T + φ) = cos where ω _{c is} the counting period of the counting means 8, ω _{IF is} the center frequency of the IF received signal, φ is an arbitrary initial phase, and π / N is the phase shift after T seconds. (2nπ + φ ± (π / N)) (1) Find a positive number n that satisfies However, the following condition is added when solving the equation (1).

Ω _IF T−π + φ ≦ ω _c T + φ = 2nπ + φ ± (π / N) ≦ ω _IF T + π + φ (2) The counting cycle of the counting means 8 is set from ω _c obtained under these conditions. Therefore, the above equation (2) is modified as follows.

F _IF − (f _s / 2) ≦ f _c = f _s (n ± (1 / 2N)) ≦ f _IF + (f _s / 2) (3) where 1 / T = f _s And

[0034] Thus as an integer _{n, (f IF / f s} ) - (1/2) ± (1 / 2N) ≦ n ≦ (f IF / f s) + (1/2) ± (1 / 2N) (4) is required.

As an example, f _IF = 500 (kHz), f _s
= 21 (kHz), modulation method is π / 4 shift differential QPS
Counting cycle f of the counting means 8 in the case of the K method (N = 4)
ask for _c . This is an example for a PDC system. In this case, the positive number n satisfying the expression (4) is 24. Therefore, the counting cycle f _c of the counting means 8 is f _c = f _s (n ± (1 / 2N)) (5) = 21000 × (24 ± (1/8)) = 501375 (Hz), 506625 (Hz).

The counting means 8 has a cycle corresponding to the former frequency.
Is operated, the operating phase of the counting means 8 after the elapse of T time is delayed by π / 4 with respect to the phase at the counting start time, and when the counting means 8 is operated at a cycle corresponding to the latter frequency, T After the lapse of time, the operating phase of the counting means 8 advances by π / 4 with respect to the phase at the counting start time. On the other hand, since the IF reception signal is modulated by the information series, the phase changes by ± π / 4 or ± 3π / 4 after the elapse of T time. Therefore, for example, when the counting means 8 is operated at a cycle corresponding to the latter frequency, π / 4 after the elapse of T time.
When the information that changes the phase is transmitted, the detected phase becomes the same at the counting start time and at the two times after the elapse of T time.

Thus, by absorbing the fixed phase change component of the shift type differential modulation system in the demodulator,
It is possible to reduce the number of code determination points, and the device can be downsized. In the above example, 8 points were required, but the judgment point was 4
Reduced to points.

Although this demodulation system is aimed at realizing synchronous detection, it is also effective for an asynchronous differential demodulation system.

FIG. 4 shows a π / 4 shift differential QP on Cartesian coordinates.
The signal point arrangement of the SK modulation method is shown. The transition from ○ to × and the transition from × to ○ are performed in the physical information transmission cycle. Therefore, XX is transmitted at every other time, and in the case of synchronous detection by the demodulator, the judgment for X and the judgment for ◯ must be made at a total of eight points every other time, and the physical information transmission cycle The code judgment standard must be changed every time.

In the demodulation device of this embodiment, a phase difference of π / 4 is generated between the operating phase of the counting means 8 and the phase of the intermediate frequency reception signal in each physical information transmission cycle, so that as shown in FIG. , The judgment point position is reduced to 4 points. As a result, detection / judgment can be performed without changing the code judgment reference for each physical information transfer cycle, the number of analog and digital parts can be reduced, and the demodulator can be downsized and consume less power. Etc. can be realized.

Further, according to the present invention, D which will be specified in the future
In the realization of the software demodulation device by the SP, it is possible to reduce the number of synchronous detection programs.

The demodulator according to the present invention can also be applied to an asynchronous differential detection system. Because
This is because as long as Expressions (1) to (5) are satisfied, degeneration of the phase of the IF reception signal does not occur and information is added only to the phase change based on the physical information transmission cycle. Therefore, the output from the sampling means 5 in FIG. 1 can be detected by the detecting means 6 as in the conventional case.

The embodiment in which the present invention is applied to a demodulator applied to a base station or a terminal station of a wireless communication system that performs communication with a signal phase-modulated by a digital signal has been described above. The present invention can be applied to a demodulation device applied to a wireless communication system that performs communication with a signal that is frequency-modulated (for example, MSK modulation method) by a signal, and similar effects can be obtained.

[0044]

As described above, according to the present invention, a base station of a wireless communication system for performing communication by a signal frequency-modulated or phase-modulated by a digital signal, particularly a wireless communication system for performing communication by a shift type phase modulation system. When a synchronous detection method is realized by a demodulator of a station or a terminal station, the phase shift peculiar to the shift type differential modulation method that occurs in each physical information transmission cycle can be absorbed, and the code judgment reference is changed in physical information transfer cycle units. It is possible to perform detection / judgment under a fixed judgment criterion without any need. As a result, it is possible to realize downsizing of the demodulator for digital wireless communication, lower power consumption, and the like.

[Brief description of drawings]

FIG. 1 is a diagram showing an overall configuration of a demodulator for digital wireless communication according to an embodiment of the present invention.

FIG. 2 is a diagram showing the configuration of the demodulation device of FIG. 1 including a detailed configuration of sampling means.

3 is a counting cycle of counting means in the demodulator of FIG. 1,
It is a figure which shows the relationship of a physical information transmission period and an IF reception signal period.

FIG. 4 is a diagram showing a signal point arrangement of a π / 4 shift differential QPSK modulation method on Cartesian coordinates.

5 is a diagram showing a code decision point arrangement on Cartesian coordinates in the demodulator of FIG.

FIG. 6 is a diagram showing an overall configuration of a demodulator for digital wireless communication adopting a conventional differential modulation method.

7 is a diagram showing a configuration of a differential detector in FIG.

[Explanation of symbols]

1 ... Demodulator 2 ... Receiving antenna 3 ... Frequency conversion means 4 ... Phase detection means 5 ... Sampling means 6 ... Detection means 7 ... Demodulation means 8: Counting means 9 ... Reference clock generation means 10 ... Amplitude limiting means 21 ... holding means 22 ... D type flip-flop

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Claims (2)

(57) [Claims] 1. A π / N shift differential N-phase PSK modulation system
In a demodulator for digital wireless communication, receiving means for receiving a signal frequency-modulated or phase-modulated by a digital signal, frequency conversion means for converting the received signal into a signal of a predetermined intermediate frequency, and a physical information transmission cycle The intermediate frequency after a unit cycle time
To a value that causes a phase shift of ± π / N between the number of received signals
Counting means that operates with a predetermined reference clock at a set cycle; sampling means that samples the output of the counting means with reference to the received signal of the intermediate frequency and outputs phase information of the received signal; 2. A demodulator for digital wireless communication, comprising: a detection means for detecting the output of the above-mentioned; and a demodulation means for demodulating transmission information from the output of the detection means. 2. A π / 4 shift differential QPSK modulation system data
In a demodulator for digital wireless communication, receiving means for receiving a signal frequency-modulated or phase-modulated by a digital signal, frequency conversion means for converting the received signal into a signal of a predetermined intermediate frequency, and a physical information transmission cycle Of intermediate frequency after unit cycle time
Set to a value that causes a phase shift of ± π / 4 from the received signal
Counting means for operating a predetermined reference clock is periodic, sampling means for outputting the phase information of the received signal output of said counting means by sampling based on the reception signal of the intermediate frequency, said sampling means A demodulator for digital wireless communication, comprising: a detection means for detecting an output, and a demodulation means for demodulating transmission information from an output of the detection means.